Page 406 - WSAVA2018
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 25-28 September, 2018 | Singapore
slightly distally into the olecranon fossa (towards the tip of the anconeal process). This is the largest joint space in the elbow.
This is probably the easiest joint to sample. There are three joint levels in the carpus;
the antebrachiocarpal (ABC) joint, the middle carpal joint and the carpometacarpal joint. The ABC joint is the most proximal of the carpal joints located between the radius and the radial and ulna carpal bones. The middle carpal joint lies between the radial and ulna carpal bones and the numbered carpal bones. The carpometacarpal joint is the most distal of the three joint levels.
The middle carpal joint and the carpometacarpal joint communicate with each other while the ABC joint is separate. Despite this, sampling is routinely made from the ABC joint as it is the largest of the carpal joint spaces and it is rare that joint disease should be localised specifically to the distal two joint levels.
The carpus is flexed and the needle is inserted into the craniomedial part of the ABC joint. A depression can be visualised and palpated at the joint space. The accessory cephalic vein is also easily visualised in this location and avoided.
Coxofemoral joint
The coxofemoral joint is more difficult to sample and is not routinely sampled unless specific indications exist. A lateral or a ventral approach is possible.
For the lateral approach the femur is abducted and slightly externally rotated (supinated). The needle is inserted craniodorsal to the greater trochanter and directed medially and slightly ventrally to penetrate the joint space.
For the ventral approach the animal should be positioned in dorsal recumbency with the stifle joint fully abducted and the femur perpendicular to the long axis of the spine. The insertion of the pectineus muscle on the ileopectineal eminence of the pubis is palpated. The needle is inserted caudolateral to this eminence and directed cranially and dorsally into the joint.
Stifle joint
When a palpable joint effusion exists the easiest collection site in the stifle is the femoropatella joint pouch, which is the largest of the joint pouches in the stifle joint. It should be noted that this is a potential space so it is only suitable for collection when an effusion is present.
The needle is inserted immediately lateral to the patella and trochlea ridge at the level of the distal pole of the patella elevated about 300 fro the skin surface. The needle is directed dorsally towards the non-articular part
of the lateral femoral condyle.
In chronic disease with thickened joint capsule you
will feel a decrease in resistance when the needle tip passes through the capsule into the joint. If the condyle is contacted by the needle (this area is not covered in articular cartilage so no damage is done), the needle is withdrawn slightly and the collection made.
The femorotibial joint space is the other option for collection from the stifle joint. It is a permanent space and so is easy to penetrate even when no effusion is present however collection of fluid can be complicated by interference by the fat pad.
The needle is inserted immediately lateral to the straight patellar ligament midway between the patella and the tibial tuberosity. The needle is directed medially and caudally through the fat pad into the intercondylar space.
Hock joint
The hock joint can be penetrated medially or laterally and either cranial or caudal to the malleoli.
What to do with the synovial fluid on collection?
What you do with the synovial fluid will depend on the volume collected.
If small volumes (<0.2ml) are obtained these should be assessed in the syringe for color, clarity and viscosity prior to preparation of a direct smear. In these cases there is not enough fluid to submit a sample in EDTA for total white blood cell count so the sample is assessed visually for color and clarity, a smear is made, and the viscosity is subjectively assessed.
Smears should be made as soon as possible after collection to reduce the artefactual vacuolation and nuclear degeneration of large mononuclear cells. Smears are simply made by placing a drop on a slide and performing a “squash” preparation where a spreader slide is laid flat on the sample slide and the two slides are drawn slowly apart. Thin smears are easier to interpret and can be made by slowly pulling the two slides apart.
If larger volumes are collected the fluid should be put into anticoagulant tubes. Unless a mucin clot test for viscosity is to be performed place a drop on a slide as described above for a smear and put 1ml into an EDTA tube.
Normal synovial fluid will not clot, as it does not
contain fibrinogen. However if there has been blood contamination during collection or intra-articular haemorrhage or protein exudation has occurred, clotting may occur.
EDTA is the preferred anticoagulant for cytological examination while heparin is preferred for the mucin clot test and viscosity measurement. EDTA will cause

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